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Biomedical subjects

A Pentland

Publications and source records attributed to A Pentland.

13 recordsLinked to original sources
PubMed2006

Nephrogenic systemic fibrosis among liver transplant recipients: a single institution experience and topic update.

Nephrogenic systemic fibrosis (NSF) is a recently characterized systemic fibrosing disorder developing in the setting of renal insufficiency. NSF's rapidly progressive nature resulting in disability within weeks of onset makes early diagnosis important. Two reports of NSF after liver transplantation are known of. We present three cases of NSF developing within a few months after liver transplantation and review the current literature. Loss of regulatory control of the circulating fibrocyte, its aberrant recruitment, in a milieu of renal failure and a recent vascular procedure appear important in its development. Known current therapies lack consistent efficacy. Only an improvement in renal function has the greatest likelihood of NSF's resolution. Delayed recognition may pose a significant barrier to functional recovery in the ubiquitously deconditioned liver transplant patient. Early recognition and implementation of aggressive physical therapy appear to have the greatest impact on halting its progression.

Aged↗
PubMed2001

Protease-activated receptor 2, a receptor involved in melanosome transfer, is upregulated in human skin by ultraviolet irradiation.

Previous studies have shown that the protease-activated receptor 2 is involved in skin pigmentation through increased phagocytosis of melanosomes by keratinocytes. Ultraviolet irradiation is a potent stimulus for melanosome transfer. We show that protease-activated receptor 2 expression in human skin is upregulated by ultraviolet irradiation. Subjects with skin type I, II, or III were exposed to two or three minimal erythema doses of irradiation from a solar simulator. Biopsies were taken from nonexposed and irradiated skin 24 and 96 h after irradiation and protease-activated receptor 2 expression was detected using immunohistochemical staining. In nonirradiated skin, protease-activated receptor 2 expression was confined to keratinocytes in the lower one-third of the epidermis. After ultraviolet irradiation protease-activated receptor 2 expression was observed in keratinocytes in the upper two-thirds of the epidermis or the entire epidermis at both time points studied. Subjects with skin type I showed delayed upregulation of protease-activated receptor 2 expression, however, compared with subjects with skin types II and III. Irradiated cultured human keratinocytes showed upregulation in protease-activated receptor 2 expression as determined by immunofluorescence microscopy and Western blotting. Cell culture supernatants from irradiated keratinocytes also exhibited a dose-dependent increase in protease-activated receptor-2 cleavage activity. These results suggest an important role for protease-activated receptor-2 in pigmentation in vivo. Differences in protease-activated receptor 2 regulation in type I skin compared with skin types II and III suggest a potential mechanism for differences in tanning in subjects with different skin types.

Adult↗
PubMed1999

Modeling and prediction of human behavior.

We propose that many human behaviors can be accurately described as a set of dynamic modes (e.g., Kalman filters) sequenced together by a Markov chain. We then use these dynamic Markov models to recognize human behaviors from sensory data and to predict human behaviors over a few seconds time. To test the power of this modeling approach, we report an experiment in which we were able to achieve 95% accuracy at predicting automobile drivers' subsequent actions from their initial preparatory movements.

Automobile Driving↗
PubMed1998

Streptolysin O and adherence synergistically modulate proinflammatory responses of keratinocytes to group A streptococci.

In contrast to a mutant adhesin-deficient Streptococcus pyogenes (group A streptococcus), its isogenic parental strain binds to human keratinocytes and promotes a vigorous proinflammatory response, characterized by enhanced expression of several cytokines, a more rapid release of prostaglandin E2 (PGE2) and damage to keratinocyte membranes. However, adherence alone is not sufficient to induce these responses. In this study, we have begun to examine the contribution of other streptococcal products in interactions with keratinocytes by the construction and evaluation of mutants deficient in expression of the secreted pore-forming haemolysin, streptolysin O (SLO). Inactivation of SLO did not prevent the streptococci from adhering to cultured HaCaT keratinocytes or from expressing an unrelated second streptococcal haemolysin, streptolysin S, during infection of keratinocytes. As measured by a quantitative reverse transcriptase polymerase chain reaction (PCR) assay, inactivation of SLO also did not have a marked effect on the expression of interleukin 1alpha (IL-1alpha) during infection. However, the lack of the ability to produce SLO was associated with a considerable reduction in expression of IL-1beta, IL-6 and IL-8 by infected keratinocytes. Measurement of the release of PGE2 by an enzyme-linked immunosorbent assay demonstrated that the SLO-deficient mutants were also not capable of promoting the rapid high level of PGE2 release characteristic of the adherent SLO-producing parental strain. Finally, analyses using the fluorescent probe ethidium homodimer-1 and measurements of release of keratinocyte lactate dehydrogenase indicated that the failure of the SLO-deficient mutants to induce responses was associated with the failure of these mutants to damage the integrity of the keratinocyte membrane. These data implicate SLO as a factor that acts synergistically with an adhesin to modulate the signalling responses of keratinocytes during infection.

Bacterial Adhesion↗
PubMed1997

Content-based indexing of images and video.

By representing image content using probabilistic models of an object's appearance we can obtain semantics-preserving compression of the image data. Such compact representations of an image's salient features allow rapid computer searches of even large image databases. Examples are shown for databases of face images, a video of American sign language (ASL), and a video of facial expressions.

Algorithms↗
PubMed1997

Keratinocyte proinflammatory responses to adherent and nonadherent group A streptococci.

The gram-positive bacterium Streptococcus pyogenes (group A streptococcus) is the causative agent of a wide variety of suppurative infections of cutaneous tissues. Previous analyses have demonstrated that the M protein of S. pyogenes is an adhesin that directs the attachment of the streptococcus to keratinocytes in the skin. In this study, we have examined keratinocyte function in response to S. pyogenes and found that adherent versus nonadherent streptococci promote distinct patterns of expression of several proinflammatory molecules and keratinocyte cell fate. When analyzed by a quantitative reverse transcriptase PCR method, infection of cultured HaCaT keratinocytes with adherent, but not nonadherent, streptococci resulted in increased expression of mRNA for the cytokines interleukin-1alpha (IL-1alpha), IL-1beta, and IL-8 but neither infection induced expression of tumor necrosis factor alpha. In contrast, both adherent and nonadherent S. pyogenes induced expression of IL-6 and each promoted synthesis and release of prostaglandin E2 (PGE2). However, considerably greater levels of IL-6 expression were stimulated by adherent streptococci relative to nonadherent streptococci and the kinetics of PGE2 release in response to nonadherent streptococci was delayed compared to the response to adherent streptococci. Staining with the fluorescent probe ethidium homodimer-1 revealed that keratinocyte membranes were rapidly damaged upon infection with adherent streptococci but were not damaged by nonadherent streptococci. Finally, treatments which inhibited streptococcal metabolism completely blocked the ability of adherent streptococci to elicit responses. These data suggest that expression of an adhesin is a strategy used by S. pyogenes to modulate keratinocyte responses during infection of the skin and implicate additional streptococcal products in these signaling interactions.

Bacterial Adhesion↗
PubMed1989

Heterogeneity of cellular expression of arachidonate 15-lipoxygenase: implications for biological activity.

Comparison of relative arachidonate 15-lipoxygenase activities in different types of human cell reveals striking differences in levels of product generation. Among available human cell types, the tracheal epithelial cell and the eosinophil have markedly higher levels of activity than other cell types with reported activity. Theories of functional significance for this enzymatic pathway will need to account for the selective expression of high levels of activity in a highly limited number of cell types.

Arachidonate 15-Lipoxygenase↗
PubMed1989

Use of injectable cultured human fibroblasts for percutaneous tissue implantation. An experimental study.

Large quantities of cultured human facial dermal fibroblasts were propagated from randomly selected patients to determine their relative suitability as percutaneously injectable living implants. Volumetric and histologic comparisons were made between the following implants that were injected subcutaneously into athymic nude mice: (1) cultured human fibroblasts (HFb); (2) cultured human fibroblasts dispersed in Zyderm II collagen (HFb + Zyd); (3) Zyderm II collagen (Zyd); and (4) Zyplast collagen (Zyp). Both the HFb and HFb + Zyd implants were accepted as primary takes but regressed volumetrically at significantly greater rates than either the Zyd or Zyp implants. Correlative immunohistochemical staining revealed that, by 10 days, 90% of the cells within the HFb implants and 80% within the HFb + Zyd implants were of human origin; however, by 9 weeks, approximately 25% of the cells were of human origin in both types of implants. These results indicated that cultured human fibroblasts can be successfully injected as living grafts; however, the subsequent gradual attrition in the numbers of implanted cells, as noted in this model system, limits the long-term retention of the implants.

Animals↗
PubMed1989

Shape information from shading: a theory about human perception.

I present evidence that people assume a simple, linear reflectance function when interpreting shading information. Using this reflectance function I derive a closed-form solution to the problem of extracting shape information from image shading. The solution does not employ an assumption about surface smoothness and so is directly applicable to complex natural surfaces such as hair or cloth. A simple biological mechanism is proposed to implement this recovery of shape. It is shown that this simple mechanism can also extract significant shape information from line drawings.

Form Perception↗
PubMed1989

A regiospecific monooxygenase with novel stereopreference is the major pathway for arachidonic acid oxygenation in isolated epidermal cells.

We investigated the enzymatic mechanisms responsible for AA oxygenation in homogenous cell suspensions obtained by trypsinization of epidermis from healthy subjects. Cell incubation with AA (0.3-150 microM) invariably resulted in the predominant generation of a compound identified as 12-hydroxyeicosatetraenoic acid (12-HETE) by HPLC and by both negative-ion chemical ionization and electron-impact mass spectrometry. Maximal amounts of 12-HETE were 126 +/- 21 pmol/10(6) cells (+/- SE), and concentration-response curves yielded half-maximal levels for 12-HETE similar to PGE2 at 2 microM AA. Two epoxyeicosatrienoic acids derived from AA were also identified. Stereochemical analysis by chiral-phase chromatography demonstrated that the epidermal cell 12-HETE was a mixture of the 12S- and 12R-hydroxy isomers in a molar ratio varying from 2:1 to 8:1 among subjects. Subcellular fractionation into 12,000 g pellet (containing mitochondria) and 100,000 g supernatant (cytosol) and pellet (microsome) demonstrated that greater than 99% of the 12-HETE was generated by enzymatic activity distributed equally in the two pellets. Both mitochondrial and microsomal activities were increased upon addition of NADPH and were inhibited by carbon monoxide, but the molar ratio of 12S/12R-HETE was threefold greater in microsomal than in mitochondrial fractions. The results demonstrate that human epidermis contains active membrane-bound monooxygenase(s) which preferentially generates 12-HETE from AA, exhibits a 12S stereopreference of hydroxylation, and suggests the presence of distinct mitochondrial and microsomal enzyme systems in epidermal cells.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗